Why Aren't We Hearing More About Ceres?

Ceres is a strange, strange world. It was first discovered in 1801, and until 1852, it was considered a planet. The discovery of numerous other bodies in its region of space, including at least a couple that were smaller but also sizeable, as well as its utter smallness compared even to dinky Mercury and Mars, led to its demotion.

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Change a few words and dates in the preceding paragraph, and you have another one of our solar system's other dwarf planets: Pluto. There is currently a craft in orbit around Ceres, the Dawn spacecraft; while Pluto just had a flyby with the New Horizons craft. There has been a lot of excitement from the little pieces of news coming out of Pluto. So why does everyone seem to shrug at Ceres?

There are a few reasons. Pluto was stripped of full-on planetary status in 2006. Most people alive grew up with Pluto as a planet. No one alive, save some tortoises, trees, and clams, grew up with Ceres as a planet. In fact, the 2006 IAU vote that made Pluto a dwarf planet also bumped Ceres up to that recognition status. Under the first draft of the IAU resolution, something else might have happened: Pluto would have stayed a planet, but Charon would have become one too, along with Ceres and Eris, a Pluto-sized world in the outer Kuiper Belt. In other words, Pluto has long been a missing piece of the planetary exploration puzzle, the one (sort of) planet that we never visited. Ceres was "just" an asteroid.

Then there's the Dawn spacecraft itself. While it entered Ceres' orbit in March, the craft is taking a slow route to Ceres, using complicated orbital dynamics to bring it to just 225 miles above the surface. Thus, news from Ceres has been a little slow to reach Earth – its primary mission is just getting underway. Its also a lot darker than Pluto, marked by fewer regions of apparent surface ice. However, there are a lot of intriguing bright spots jutting out from its surface that shine from Ceres, indicating the presence of what is either water or salt.

The spacecraft also suffered a glitch that sent it into safe mode right around the same time New Horizons did. But since the craft was in orbit (rather than performing a quick flyby), the Dawn team could afford to let it linger in safe mode a little longer. This means that the data collection itself is a slower process, and that, during the Pluto flyby, the Dawn spacecraft was under repair rather than actively gathering info.

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So while Pluto is getting the spotlight, we should afford Ceres a little time to shine. Ceres is looking like a more fascinating and complicated world than we ever anticipated, which sounds a lot like Pluto. And like Pluto, it shows signs of recent geologic activity, potential oceans, and a tenuous atmosphere. Unlike Pluto, it's warmer and some of its ices may have the consistency of a snowball.

Astrophysicist Andy Rivkin tweeted a few intriguing tidbits about Ceres from the NASA Exploration Science Forum today. The first is that while not as active as Pluto on the surface (it doesn't have an object half its size tugging on it as Charon tugs on Pluto), the bright spots are signs of some kind of activity on the world. There also appears to be a haze emanating from them, which could be the sublimation of liquid. As Alexandra Witze writes in Nature, this could mean that the material of the bright spots is ice and not salt, which further bolsters the strong arguments for water (and a possible ocean) on Ceres.

The famous bright spot photo shows the "most complex set" of bright spots, but they appear all over the world, which had been demonstrated in previous photos from the Dawn spacecraft. The spots are variable in size and shape, have uneven distribution, and don't appear to be the result of a collision, which means they may be jutting out from below the surface.

There's are a few other things Dawn has learned. For instance, the poles on Ceres are flipped from what was anticipated, meaning that the seasons are reversed from what previous models showed. It's also smaller in diameter and denser. The "pyramid" object spotted recently is likely similar to the ice mountains on Pluto.

By next month, the spacecraft will be less than 1000 miles from the surface. Likely by the end of the year, it will enter its closest orbit, where it will remain stably even after the mission is over. There's a lot to learn about Ceres, including whether it's maybe – just maybe – another place to look for life in our solar system.

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